1. Field of the Invention
The present invention relates to an electrode for use in the treatment of an object such as a semiconductor wafer or the like with a plasma treatment process such as plasma etching, plasma CVD (chemical vapor deposition), or the like.
2. Description of the Relevant Art
Known apparatus for treating an object such as a semiconductor wafer through plasma reaction have a hermetically sealed reaction chamber in which a pair of vertically spaced electrodes is disposed, as disclosed in U.S. Pat. Nos. 4,318,767 and 4,336,438. The object to be treated is placed on the lower electrode, and then the reaction chamber is evacuated, followed by introduction of a reaction gas into the reaction chamber. Then, a high-frequency voltage is applied between the electrodes to generate a plasma in the chamber for etching a film of SiO.sub.2, for example, coated on the surface of the object.
Electrodes employed in such conventional plasma treatment apparatus are made of a metallic material such as an aluminum alloy, stainless steel, or the like. Japanese Laid-Open Patent Publication No. 52-142971 discloses an electrode made of carbon. Another electrode disclosed in Japanese Laid-Open Utility Model Publication No. 63-3138 is made of sintered aluminum powder.
Known metallic electrodes used in the plasma treatment apparatus are, however, disadvantageous in that the metallic material of the electrode is etched or sputtered by the plasma, and atoms emitted from the electrode tend to be attached to the surface of the object, thus contaminating the same. The known carbon electrode also has problems in that the electrode surface is modified and made less durable by a plasma discharge. Also, the plasma discharge scatters around minute particle of the carbon electrode which are likewise responsible for the contamination of the object. The contamination of the object with the electrode material may be prevented by coating the electrode surface with a layer of quartz. However, quartz produces oxygen when etched, and the oxygen is apt to have an adverse effect on the plasma treatment process.